The invention relates generally to fluid gauging which involves the measurement of the mass and/or volume of fluid in a container. More specifically, the invention relates to the measurement and calculation of fluid volume and mass by numerical methods utilizing a number of pressure sensors disposed in the container.
Various fluid gauging techniques are well known and include the use of capacitive level sensors, ultrasonic level sensors and optical level sensors. Although pressure based fluid gauging has been discussed, as in, for example, U.S. Pat. Nos. 4,553,216; 4,739,494; and 5,138,559 the entire disclosures of which are fully incorporated herein by reference; such systems typically involve either numerous pressure sensors and/or a determination of the location of the liquid surface plane. Once the liquid surface plane is located, tank characterization data is used to determine the liquid volume and mass. Such known techniques tend to be rather complicated and may involve significant processor computations and extensive tank characterization data.
The objectives exist, therefore, to provide techniques for pressure based fluid gauging that are less complex and less costly to implement without loss of accuracy.
The present invention contemplates, in one embodiment, a method for gauging liquid in a container, the method comprising:
a) assigning a local three axis coordinate system for the container;
b) dividing the container into a plurality of regular volumes;
c) disposing a first pressure sensor at a predetermined coordinate proximate the bottom surface of the container, with said pressure sensor producing an output related to detected fluid pressure at said predetermined coordinate;
d) assigning to each of said volumes a corresponding volume location coordinate;
e) numerically determining, for each of said regular volumes, a corresponding liquid mass value therein based on a relationship between said detected pressure at said predetermined coordinate and a calculated pressure at each of said volume location coordinates; and
f) summing all of said numerically determined liquid mass values corresponding to said regular volumes to produce a total fluid mass value for the container.